The Modality Principle states that people learn best from visuals and spoken words, rather than from visuals and printed words.
Putting the Modality Principle into practice:
Your high school English teacher might take great offense to this: Limit the amount of text on the screen. Instead, use visuals to convey information with audio narration where possible.
Obviously, this principle doesn’t work for many situations, such as defining key terms, listing steps of a process, providing directions, etc. However, it does mean you should use audio narration when you can, as this is less likely to overwhelm learners with too much text.